The boat, El Almirante, was carrying 170 passengers and three crew members, said Margarita Moncada, the head of disaster relief for Antioquia province.

Authorities were also unsure if all the people reported to be on the boat had actually been on board, she added.

Officials initially reported nine people dead and 28 missing, but Ms Moncada said some survivors rescued by private boats were taken to different docks on the reservoir shore and so were not immediately accounted for.